These studies use neuroethological and ethopharmacological methods to investigate the mechanisms involved in the production and perception of the isolation call and related vocalizations in nonhuman primates. They provide a model for understanding the neurology and physiology of vocal expressions of affect in human infants and the impact of crying on listeners. Major findings this year were as follows: 1. Receptors for oxytocin were revealed with autoradiography in portions of limbic, striatal and olfacto-striatal regions of the brain of common marmosets. In marmoset neonates, portions of the cerebral cortex were labelled, as well, suggesting that oxytocin receptor distribution in the brain changes during development. 2. Systemic administration of an alpha-adrenoreceptor antagonist, prazosin, to adult common marmosets resulted in an increase in territorial behavior and a decrease in affiliative behavior (grooming and isolation calls). A parallel study using adult squirrel monkeys also found that prazosin decreased isolation calling. These findings suggests that the alpha-adrenoreceptor plays a role in regulating behaviors related to social affiliation and territorial defense. 3. A follow-up study of earlier work of the role of cholinergic mechanisms in mediating defensive behavior in squirrel monkeys confirmed that adult females respond more strongly to mildly alarming stimuli than adult males. A full dose response curve for benactyzine HCl, a cholinergic receptor antagonist, was established for males and for females, and indicated that the dose/response curves for both sexes are similar, but that females have a lower threshold dose for exhibiting drug-related increases in alarm behavior.